Organophosphate (OP) toxicity has acute and chronic components. Although the acute toxicity is through the known mechanism of action of OP's, the inhibition of cholinesterases, the chronic apparently is not. Recent research has suggested that the chronic toxicity is through the production of free radicals, and that this may be particularly damaging during fetal brain development. One way in which the brain responds to an increase in free radicals is through an astrogliotic reaction, which includes release of S100B. S100B is a trophic factor promoting both serotonin terminal outgrowth and synaptogenesis. Thus, in fetal OP toxicity, there will be an increase in serotonin terminals and synaptic density at a young age, but as the animal ages, both will be prematurely lost. In tests of learning and memory, therefore, the young animal may show no deficits, but the older animals, with loss of synapses, will show deficits. The proposal uses a model of OP toxicity previously found to increase serotonin and synaptic markers at a young age- injection of 1 mg/kg of chlorpyrifos (CPF) to rats on gestational days 17-20. The hypothesis will be tested as follows: Specific Aim 1: Using immunochemistry, gestational day (GD) 20 rat pups or mice will be examined for S100B content. Heat shock protein (HSP) -27 and clusterin will be used as markers of oxidative stress and microglial activation as a marker of neuroinflammation. Findings will be compared with litters given a Vitamin E-enriched diet, as an antioxidant Specific Aim 2: Using immunocytochemistry, the hippocampus will be examined for serotonin terminal density, S100B content and changes in astroglial and microglial morphology. Animals will be tested at three ages: postnatal days (PND), PND 35 (adolescence), PND 60 (adult) and PND 365 (aged). Specific Aim 3: Synaptic density will be determined at the same ages, first using immunocytochemistry of microtubule-associated protein (MAP)-2 and synaptophysin. Any changes observed will be confirmed with electronmicroscopy. Specific Aim 4: Animals will be tested for changes in learning and memory at PND 35, 60 and 365. [unreadable] [unreadable] [unreadable]